This invention relates to an X-ray generator having an automatic gain controlled circuit for stabilizing the X-ray intensity.
Conventionally, a stabilizing circuit for an X-ray generator as shown in FIG. 1 is generally used, in which a high voltage output of a constant voltage source 4 is applied between the anode 2 and the filament (or cathode) 3 of an X-ray tube 1 while the filament current is supplied from an adjustable current source 5. In such a system, by setting the anode-cathode voltage (X-ray tube voltage) to V and the anode current (X-ray tube current) to i, the value of i is dependent on the filament current I.sub.f and the voltage V. The X-ray intensity I is shown as follows, setting the minimum excited potential to V.sub.0 and wherein K.sub.1 and K.sub.2 are constants: EQU I(V)=K.sub.1 (V-V.sub.0).sup.3/2 ( 1) EQU i(i)=K.sub.2 .multidot.i (2)
If V and If are kept constant, the X-ray intensity I is stabilized for a while, but the anode current i will drift on account of the temperature rise of the X-ray tube. And accordingly, the intensity I will change in accordance with the equation (2). For compensating this change, a current detector 6 is provided to determine the anode current i which current signal is fed to the current source 5 through a feedback circuit 7 to control the filament current If so that the anode current is kept constant. Nevertheless, this conventional feedback device cannot compensate for X-ray intensity changes occurring over a long time period due to the X-ray tube deterioration (particularly due to contamination). Further, it cannot solve problems of fluctuation of X-ray intensity actually received by an X-ray detector 1a, since the X-ray intensity reaching the detector 1a is made somewhat feeble on account of X-ray absorption by air and the absorption rate changes in response to changes in air density which are dependent on atmospheric pressure and temperature.